Signaling Ranges and Characteristics

 Introduction.  Remember, network communications are made via a large range of electromagnetic wave frequencies using "wires" or "wireless" transmissions.  An electromagnetic wave is the physical form of energy described by the electromagnetic spectrum.  The spectrum starts at zero oscillations, rises through the range of frequencies that can be perceived by human senses through the various forms of light, up to the frequencies called X-rays and gamma rays.   The rates of frequency are measured in Hz - Hertz.  This is directly related to the wavelength, which can vary from billionths of a meter to several meters.  For whatever reasons, Hz are usually used for lower frequency bands and wavelengths are usually used when talking about higher frequency phenomena such as light.  The standard names and ranges/bands are given in the following diagram.

 Notice how the visible range is very very small.  We now need to quickly define a few terms which you have hopefully seen before. All signals consume some of their own energy to overcome the resistance inherent in the transmission media.  They also tend to disperse or radiate as they move. This reduction in signal strength is called attenuation. Attenuation increases at higher temperatures and higher frequencies. Attenuation is usually the main reason there are upper limits on cable lengths in different networks. As signals travel they are subject to the influence of other influences such as noise, the ballast of fluorescent lamps and whatever.   The impact these other influences incur, unwanted modification of signals in transit, is called distortion or EMI - Electromagnetic Interference. Crosstalk is a particular type of interference where signals from wires in close proximity bleed over one another. Another important characteristic of an electromagnetic wave/signal is how easily it is broken up or how frangible they are.  For example, radio waves can penetrate and be received through all but the densest materials. Directionality has to do with how well a signal can be focused towards a particular location.  This capability increases with the frequency Bandwidth is the maximum amount of data that can be carried over a specific transmission media. Now we need to state one basic principle. The lower the frequency, the lower the potential for carrying data because there are fewer state changes per unit time.  While this does not really correspond to how data, it is reasonable to think that one bit of information can be transmitted per cycle. The following tables contain some of the most important signal characteristics for low and high frequencies.

 Low Frequencies persistent signal more durable more penetrating less frangible FCC regulated due to the above low bandwidth broad radiation

 High Frequencies more frangible high bandwidth potential for tightly focused transmission